The goals of this amended project are directed toward the immunobiology of normal and neoplastic lymphocytes, the role of the major histocompatibility complex (MHC) in immune regulation and the cytogenetics and biology of human lymphoid tumors. Specifically, the component projects deal with studies of (1)\the function and specificity of cloned murine T cells, (2)\the origin of diversity in the T-cell repertoire and various aspects of lymphocyte specificity and function in chimeric mice, (3)\the control by MHC gene products of replication of leukemogenic virus in cultured cell lines, and (4)\the genetic and biological changes associated with human lymphocytic leukemia.